Newt Gingrich has made questions about President Barack Obama and the president’s “attacks” on the Roman Catholic Church a central theme of his campaign. So has Rick Santorum.

Both turned up the burner on the rhetoric last week — Gingrich by asking why Obama does things that make voters question his religion, and Santorum by unveiling an ad — that spliced images of the president with Iranian strongman and Holocaust denier Mahmoud Ahmadinejad. Santorum’s team says the visual juxtaposition was unintentional.

Of the four remaining prominent hopefuls who have won states in the GOP primary, Mitt Romney is the one who has steered clear of stoking the embers within the Republican Party that insist Obama is a Muslim. It’s an untruth about the Christian president that never totally disappeared after 2008 and is back for a second airing.

Beyond a survey from the Democratic firm Public Policy Polling, which provocatively asked GOP primary voters in Mississippi and Alabama whether they think Obama is a Muslim — about half of the Republicans in each state said they do — there is no quantifiable data indicating whether this view is widespread.

Yet Romney may inherit the issue as the party’s likely nominee should the same voters — who will never support Obama — show up at his rallies in the fall. And the question will be not just how it presents itself, but how Romney beats it back.

“What the Romney team should be doing is watching this [at their rivals’ rallies] and trying to figure out how they’re going to handle it,” said a veteran Republican strategist and alumnus of presidential races, adding that Gingrich’s approach bothers a majority of Republican surrogates, strategists and candidates.

In recent weeks, both Gingrich and Santorum have faced voters at their rallies who erroneously believe that Obama is a Muslim. Both Republicans have, to varying degrees, taken a pass on the chance to swat down those comments. Gingrich, especially, has intensified the inflammatory rhetoric.

“I think it’s absurd to talk the way Newt did,” said Charlie Black, a former John McCain strategist who is now an informal Romney adviser. “If he thinks he’s playing for votes, that’s absurd. It crosses the line of civility. On matters of race and religion, people running for national office have an obligation to be extremely careful not to get near a line of race and religion, let alone [cross] it.”

“They certainly know what John did,” Black said, referring to McCain’s flat rejection of the allegations that Obama was a Muslim in 2008, adding that Romney doesn’t engage in spreading conspiracy theories.

Three sources close to the Romney campaign said this week that they’re not aware of any internal discussions on how to address the inevitable: people showing up at Romney rallies, when he is the Republican nominee, expressing inflammatory rhetoric about the president.

Several sources pointed out that the election will hardly pivot on this issue but will instead be fought on the economy.

More than any other presidential candidate, Gingrich has played to this issue. At a rally in Louisiana last week, he failed to set the record straight when a voter asking a question declared the president is “a Muslim” who is trying to ruin the country.

Gingrich responded that he believes Obama is a “Christian” who was “listening to sermons” when he attended a Christian church for 20 years. But the ex-House speaker then seemed to blame Obama for sowing doubt among voters about his religious sympathies.

“The fact is I take him at his word, but I think it is very bizarre that he is desperately concerned to apologize to Muslim religious fanatics while they are killing young Americans while at the same time going to war against the Catholic church and against every right-to- life Protestant organization in the country. I just think it’s a very strange value system,” Gingrich argued.

Obama’s policy, as Gingrich described it? “They’re just standard, left-wing values, which is as long as you’re not Christian or Jewish, we respect you.”

And this: “Why does the president behave the way that people would think that [he’s Muslim]? You have to ask, why would they believe that? It’s not cause they’re stupid. It’s because they watch the kind of things I just described to you.”

Gingrich spokesman R.C. Hammond insisted to POLITICO that Gingrich is not attempting to stoke fear among voters about Obama. Yet Hammond also tweeted after his boss’s news conference, “As long as the President gives people reasons to doubt — they will doubt.”

Meanwhile, Santorum said on Sean Hannity’s radio show last Friday that Obama has “embraced radical Islamic groups.” Around the same time, the former Pennsylvania senator’s campaign released a Web video showing a bleak future for America if the president stays in office, interspersing an image of Obama with one of Ahmadinejad.

Santorum has insisted he is not taking issue with Obama’s religion. “If he says he’s a Christian, he’s a Christian,” he has said, a means of taking the president at his word without stating so definitively.

The man behind the video, longtime Santorum adviser John Brabender, insisted to POLITICO that there was no intent behind splicing Obama with Ahmadinejad. And indeed, Santorum has been talking about “radical Islam” for years, including in his losing 2006 Senate race. Meanwhile, Gingrich’s attention-getting comments are more overt and are timed to grab headlines as his campaign appears to be on its final legs.

But the inflammatory comments have renewed focus on an idea that has never disappeared among a small group of right-wing voters who will never back Obama. The intense concern about Iran’s alleged attempt to build a nuclear weapon is serving as a fig leaf for some of the anti-Muslim hysteria.

It is language that many former George W. Bush advisers have spent years trying to quash, trying to delineate the “war on terror” from a war on Islam itself.

Peter Wehner, a former George W. Bush speechwriter and adviser who is now a senior fellow at the Ethics and Public Policy Center, described the PPP poll results as “startling.” Wehner said the issue arose again in the 2012 cycle when Herman Cain said he wouldn’t appoint a Muslim to his Cabinet because he was afraid it would open the door to imposing Shariah law on the country.

“It’s a proxy for, it’s a manifestation for antipathy for President Obama,” Wehner said. “For some people who are Christians, they don’t believe you can be Christian and politically liberal. … For people who believe [Obama is Muslim], they think being a Muslim means being sympathetic to terrorists.”

As for Romney, Wehner said he thinks he’ll “take a page from Sen. McCain.”

“The morally right thing and the politically [wise] thing to do” is to denounce and reject it, he said.

But the talk about Obama being a Muslim is a way of describing Obama “as the enemy within,” said a Republican strategist who expresses disgust at the claim. Another said that the way Gingrich and, to a lesser extent, Santorum have talked about Islam and the context of religion have enabled voters who don’t support Obama’s policies to undermine him on other grounds.

Tom Jensen of PPP said, “Saying Obama is a Muslim … is sort of a combination of genuine lack of knowledge or understanding about the president’s religion and the sort of aspect of, ‘We don’t like this guy, so we’re going to say he’s a Muslim.’ They don’t want to accept that he’s an American just like they are.”

Black, the Romney adviser, suggested the results of that single poll showing half of Mississippi and Alabama GOP voters think Obama is a Muslim are being overblown: “There’s probably more people who believe in UFOs than believe that.”

Romney may not accept talk of religious intolerance, but his footing is less firm when it comes to those voters who doubt the authenticity of Obama’s birth certificate. Despite the fact that the president has produced the long form document, “birthers” who doubt his U.S. nationality still exist.

Romney has embraced Donald Trump as a campaign surrogate, and the real-estate mogul remains the most famous face tied to “birtherism.” Trump has questioned, even after the long form was made public, why it took so long to come to light.

Since 2008, the extreme element of Republican Party crowds has led to a series of distractions for GOP candidates.

McCain, during a September 2008 town hall meeting in Minnesota, famously interrupted a woman who insisted Obama was an “Arab” by telling her the president was, in fact, not.

“No ma’am,” McCain said at the time, telling the voter that Obama was a “decent” man with whom he had substantive disagreements.

While the move allowed McCain to claim some moral high ground by shutting down the woman’s argument, the repeated insistence from some at McCain rallies that Obama was somehow “other” than American continued to distract, said one operative who worked on the campaign.

“A moment will arise, and in that moment it will be important for whoever the nominee is to make sure they are focusing on the matters in the race and drawing that out,” the operative said. “My counsel would be: One, you need to be prepared for the moment and be ready for it, and don’t be caught flat-footed.”

The operative continued: “If it’s not based on [Obama’s] policies and his ideologies and someone is out there hatefully describing the president, you’ve gotta call bull—— on him. People will respect that. At the end of the day you can only get wrapped into so many political contortions. You have to do the right thing.”

Multiple McCain sources say questions about Obama’s religious roots — first floated in the Washington Times early in 2007 — were never something McCain wanted to exploit.

Correcting a misguided voter, another Republican operative said, could be a “Sistah Souljah” moment for Romney, giving him the chance to pivot in such a way that it will make “a lot of independents’ hearts beat a little faster.” And Romney has his own religious issue — his Mormon faith and concerns evangelical voters have expressed about it.

The voters who believe the president is Muslim “have probably already decided to vote against [Obama] in November,” said the operative.

And for Romney to address the issue of religious tolerance in a way that is relevant to skepticism about his Mormon faith could work in his favor if it’s done from a position of strength. Rather than wait for the issue to arise at a forum like a town hall, Romney could address the issue in an interview, on his own terms. In the 2012 campaign, where YouTube moments can quickly destroy a candidacy, most voters at candidate forums will most likely be pre-screened, but that’s an unknown.

There is also the chance that some of the same voters who show up to yell about Obama may take issue with Romney’s Mormonism, a number of Republicans acknowledged privately. Romney has not done what he did in 2008, when he gave a speech about religion and tolerance. But last fall he did denounce the “poisonous language” of a Rick Perry supporter who had called Mormonism “a cult.”

Steve Schmidt, a top strategist on McCain’s 2008 campaign, said that part of the problem for Republicans is a false sense of accountability for everyone who shows up at an event.

“When the media demands that the Republican candidate be answerable for every crazy person in the country who opposes the president’s policies or opposes the president for whatever reason, no matter how disgusting, it makes it impossible for the Republican candidate to A) run a race, and B) it squeezes out the ability to have a debate” on policy.

McCain, he said, handled the issue the way he did at a town hall “because he’s a person of character.”

In the case of Gingrich, Schmidt said, the “divisive” rhetoric is coming from someone with a history as a firebrand and the system has worked.

“The Republican Party has rejected his candidacy,” Schmidt said.

Similarly, Santorum has argued that it’s not his responsibility, nor should he be held responsible, for everything that gets said at one of his campaign events by an attendee.

Jarrod Agen, who served as communications director for Sharron Angle’s 2010 Senate campaign, agreed that the GOP nominee must push back on false allegations about Obama, particularly when they are made one on one or in a small-group setting.

“These clips play over and over again,” Agen said. “It shows your character and your control if you’re able to take charge of the situation, no matter how passionate people in the room may be.”

But Agen said it’s best not to engage with a loud crowd shouting things about Obama.

“It happened a lot in Nevada that people were shouting things at Sharron when she was on stage,” Agen said. “You don’t want to exacerbate things by yelling back at the crowd. But in a one-on-one basis, it’s certainly best for the candidate to set the record straight.”